Motor driven line feeds and paper insert mechanisms have existed in the prior art for a considerable period of time in different forms. An example of a device for feeding paper and which utilizes a program control in a printer is U.S. Pat. No. 2,138,646 to Scharr, showing a gear driven powered paper feed mechanism. This device is incapable of disconnection to allow easy manual feeding by hand turning of the platen.
Other examples of paper insert and line feed drive include Aebi, U.S. Pat. No. 3,960,258, which utilizes a clutch arrangement which is disengaged at the end of the desired paper insertion cycle in response to a mechanically activated linkage. In all other respects, the platen is indexed using a conventional pawl and ratchet platen indexing scheme and the gear drive arrangement is only used for paper insert and/or eject.
Another example of a gear driven line feed mechanism is Blum, U.S. Pat. No. 4,031,995, utilizing a gear driven arrangement for rotating a paper platen with a stepping motor while at the same time controlling a paper bail, facilitating paper insertion. The platen is disclosed as connected to the stepping motor and not freely manually rotatable to facilitate positioning of the platen.
It is desirable in printers to be able to electronically control the line feed through a direct motor drive and gear train arrangement to the platen for smooth continuous paper feed and paper insertion as well as for well controlled line feed of multiple increments representing lines, fractions of lines and multiple lines.
At the same time in a typewriter, it is highly desirable to be able to manually insert or position a paper within the typewriter by rotating the platen knob. It is highly undesirable, from a human factors standpoint, to have to overcome the resistance of a significant portion of the typewriter drive train including other elements unrelated to the paper feed drive in order to rotate the platen.